The present invention relates to a hydraulic control system for an automatic transmission for an automotive vehicle having an engine with a fuel-cut control which interrupts the fuel supply to the engine.
Engines are known which are equipped with a fuel-cut control which interrupts the fuel supply to the engine as long as the engine revolution speed is higher than an upper predetermined value after an accelerator pedal has been released or a throttle opening degree has been closed to cause an automotive vehicle to begin an engine braking operation. The fuel-cut is released to resume the fuel supply when the engine revolution speed has dropped to a lower predetermined value. The fuel-cut control of the above-type is known from Japanese patent publication No. 54-2339 or U.S. Pat. No. 4,221,193 issued to Ezoe et al. on Sept. 9, 1980. In adapting the engine with the fuel-cut control of the above-type to an automatic transmission of an automotive vehicle, for preventing the engine from stalling, the fuel supply is resumed immediately after a manual valve of a hydraulic control system of the automatic transmission has been shifted from a forward drive position to a neutral position to establish a neutral state where the engine is not driven by driven wheels of the automotive vehicle. The known fuel-cut control is not satisfactory in that the above mentioned lower engine speed value has to be set high enough for enabling the engine to restart should the manual valve be shifted from the forward drive position thereof to the neutral position thereof after the vehicle speed has dropped to a vehicle speed value at which the engine revolution speed is near and slightly above the lower predetermined engine speed value. If this lower predetermined engine speed value is set satisfactorily low with a view to fuel economy, the engine can hardly start upon resumption of the fuel supply after the manual valve has been set to the neutral position during operation at engine revolution speeds near the lower predetermined engine speed value. This is because when the neutral position is established in the transmission, a reverse driving force, a rotational force by which the engine is driven by driven wheels of an automotive vehicle during an engine braking, is lost and the engine revolution speed drops to a low value upon resumption of the fuel supply, thus making it difficult for the engine to start.